Introduce initial plumbing for type promotion in fasta.

pkg/front_end/testcases/inference/local_reference_upwards_local.dart

Index: pkg/front_end/testcases/inference/local_reference_upwards_local.dart
diff --git a/pkg/front_end/testcases/inference/local_reference_upwards_local.dart b/pkg/front_end/testcases/inference/local_reference_upwards_local.dart
new file mode 100644
index 0000000000000000000000000000000000000000..498778d471343a395ff471c4cfc99ffc8d89a3c9
--- /dev/null
+++ b/pkg/front_end/testcases/inference/local_reference_upwards_local.dart
@@ -0,0 +1,12 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+/*@testedFeatures=inference*/
+import 'dart:async';
+
+main() {
+  Future<int> futureInt = null;
+  var /*@type=dart.async::Future<dart.core::int>*/ x =
+      /*@promotedType=none*/ futureInt;
+}